1. Field of the Invention
This invention relates to a blade actuating apparatus for optical instruments in which a plurality of blades are actuated so that the size of an optical path aperture is changed while maintaining a similar figure.
2. Description of Related Art
As blade actuating apparatuses for cameras, of blade actuating apparatuses for optical instruments, shutter apparatuses, stop apparatuses, filter apparatuses, and lens barrier apparatuses are known. As for blade actuating apparatuses for projectors, blade actuating apparatuses for microscopes, and blade actuating apparatuses for illumination instruments, stop apparatuses are known. In the shutter apparatuses or stop apparatuses, of these, particularly designed so that a plurality of blades are actuated at the same time and the size of the optical path aperture is changed, with the optical axis as a center, it is considered ideal that the size of the optical path aperture is changed while always maintaining the similar figure close to a circle. However, in order to force such actuation upon the plurality of blades, it is necessary to provide a ring member (a driving ring in the shutter apparatus or a stop ring in the stop apparatus) reciprocated and rotated, with the optical axis as a center, so that the blades are rotated in the same direction at the same time. Hence, this structure has the problem that a high cost is caused and has recently been adopted only in a high-grade instrument.
Thus, as alternatives to the structure, blade actuating apparatuses each designed so that the size of the optical path aperture is changed, with the optical axis as a center, by a plurality of blades without providing the ring member such as that mentioned above have been numerously proposed and used. Most of these apparatuses, however, are not able to satisfy both requirements that the size of the optical path aperture always maintains the similar figure and can be continuously changed. An example of such a structure is disclosed in Japanese Patent Kokai No. 2000-352737. A stop apparatus (a light-amount adjusting apparatus) disclosed here has a unique structure and is constructed so that two stop blades (moving blades) are actuated simultaneously in directions perpendicular to each other by a single electromagnetic actuator in a plane perpendicular to the optical axis and thereby the area of the optical path aperture is changed. The present invention relates to this type of blade actuating apparatus.
Kokai No. 2000-352737, as mentioned above, discloses the stop apparatus constructed so that the two stop blades are actuated simultaneously in directions perpendicular to each other in a plane perpendicular to the optical axis and thereby the area of the optical path aperture is changed. Since the optical path aperture is provided at a place where grooves configured on the two stop blades intersect, the optical path aperture provided in this way has the shape of a square. In Kokai No. 2000-352737, it is also disclosed that the stop blades are configured so that the widths of the grooves are changed gradually, and thereby optical path apertures of a plurality of squares of different sizes can be obtained. Hence, this stop apparatus is such that the optical path aperture of the similar figure with the optical axis as a center is obtained. However, the size of such an optical path aperture is governed by the width of the groove previously configured and thus the size other than that of the preset optical path aperture cannot be obtained. Consequently, such a structure cannot be adopted in a stop apparatus designed so that the optical path aperture is continuously controlled. In addition, this structure cannot be also adopted as the shutter apparatus.